Update ci-doctor and issue-monster workflows to use gpt-5-mini

[Copilot]

Configures both CI Failure Doctor and Issue Monster workflows to explicitly use the gpt-5-mini model.

Changes

• ci-doctor.md: Added engine configuration with gpt-5-mini (previously used default)
• issue-monster.md: Updated from simple string format to structured engine config with gpt-5-mini

# Before (issue-monster)
engine: copilot

# After (both workflows)
engine:
  id: copilot
  model: gpt-5-mini

Both .lock.yml files regenerated with model references in metadata, CLI invocations, and environment variables.

Original prompt

Update cli failure doctor and issue monster to use gpt-5-mini

Custom agent used: agentic-workflows
GitHub Agentic Workflows (gh-aw) - Create, debug, and upgrade AI-powered workflows with intelligent prompt routing

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